ZHY Gear takes the transmission helical gear of subway vehicles as the research objective, and analyzes in detail the distribution and variation of tooth root stress of the helical gear pair for the operating conditions of subway vehicles; A widely applicable and computationally convenient cylindrical gear bending fatigue life prediction model was established based on the linear damage accumulation theory and energy accumulation curve, and the effectiveness and applicability of the model were verified through experiments; A single tooth meshing model of helical gears was established, and finite element method was used to analyze the root stress and fatigue of helical gear pairs for subway vehicle transmission with different modification coefficients, and the accuracy of the results was verified; According to the principle of equal strength, optimize the transmission helical gear of subway vehicles with fatigue performance as the objective through the line graph method.
The main conclusions obtained are as follows:
(1) When the helical gear pair of subway vehicles is engaged, the meshing of the helical gear pair alternates between a two tooth meshing state and a three tooth meshing state. The proportion of the two tooth meshing state is very small, about 15%. The maximum bending stress at the tooth root in a two tooth meshing state is greater than that in a three tooth meshing state. During the operation of subway vehicles, the maximum root bending stress of helical gears is greater than the fatigue limit of the material only within the speed range of 0-50km/h. This speed range plays a major role in the accumulation of fatigue damage caused by helical gear bending.
(2) The bending fatigue test of helical gears under single stage load shows that the large tensile stress near the tooth surface causes root opening cracks, and the fatigue life of the large crack propagation stage is often 10% lower than the full crack propagation life. Therefore, the initiation life of helical gears can be considered as the fatigue life of helical gears.
(3) Static analysis of a single tooth meshing finite element model of a helical gear shows that the stress distribution is relatively uniform in the tooth meshing area, which can accurately calculate the root stress of the helical gear. Comparing the root stress of the small gear with the calculation results in the GB/T 3480 method, the error is only -1.127%, and the root stress error of the large gear is only 5.387%. Therefore, this can meet the accuracy requirements for root stress calculation.
(4) For subway transmission helical gear pairs, when the coefficient of variation changes from small to large within the allowable range, the root stress of the small gear will first decrease to a certain value and then increase, while the root stress of the large gear will first decrease to a certain value and then slightly increase to a certain value before decreasing again. The maximum tooth root stress point of the large gear is always located at the tooth root position corresponding to the farthest distance from the tooth root on the meshing line. There are two types of positions for the maximum stress at the root of the small gear, which are located at the tooth root position corresponding to the farthest distance from the meshing line to the tooth root, and at the tooth root position corresponding to the distance from the meshing line to about one-third of the far end of the tooth root.
(5) The minimum error of tooth root stress obtained by the line graph method is 0.02%, and the maximum error is 1.51%; The minimum error in the fatigue life of the obtained helical gear is 0.59%, and the maximum value is 18.76%. Prove that the line graph method can accurately predict the root stress and fatigue life of subway transmission helical gear pairs under different modification coefficients.
(6) According to the principle of equal strength, the comprehensive fatigue life of the subway transmission helical gear pair optimized using the line graph method is 3.29 times that of the prototype helical gear pair, which is better than the principle of equal life. When using the line graph method to optimize the modification coefficient of helical gears, priority should be given to the principle of equal strength.
There are some shortcomings and limitations in ZHY Gear research, and further supplementary research is needed in the following areas:
(1) Only the bending stress and fatigue life of the subway transmission helical gear were studied under two different tooth numbers, while the other tooth numbers were not involved. It is necessary to study the variation law of the bending stress and fatigue life with the variation coefficient for different tooth numbers of more models of subway vehicles.
(2) Due to the fact that the bending fatigue test of helical gears in the study is conducted on equivalent spur gears, in order to make the prediction model for bending fatigue life of helical gears proposed in Chapter 3 more applicable and accurate, bending fatigue tests on helical gears should also be carried out.